Stereo sound on TV channels is very similar to the way it's done on FM radio stations. There's a double sideband L-R at a supressed carrier twice the horizontal deflection frequency. There is also a pilot tone which is the same as the horizontal freq. FM radio uses 38 and 19KHz for these.

Only real difference between FM radio and TV sound is that the L-R signal has DBX noise reduction applied to it. But some early stereo TV sets didn't worry about this. It would sound something like a dolby tape played without dolby.

But one could modify an existing tube FM stereo decoder, as shown below. And it should work reasonably well.

...

Shove come to push you could always run a VCR as the stereo source. This would also give you remote channel selection, just leave the set on ch. 3 of course. Seems to me that this will be the solution to when broadcasters switch to digital.

Anthony

Should have mentioned it, but I was thinking of "What if stereo TV existed back in the early 60's. What would they have built to receive it?" Perhaps they would have had the FM stereo detector circuit do double duty, with relays or such switching the resonance of the tuned circuits from 19 and 38KHz to 15.7 and 31.4KHz. Probably switching extra capacitence like my mods above.

This would apply to those big consoles with the stereo FM and record player and of course the 25" color TV. If I had one, I'd be tempted to build this mod into it....:)

...

Somewhere in my attic is a Recoton stereo adaptor that they sold over 10 years ago. It was about half the size of a VCR and had a small, wired stick-on probe (coil ?) that you attached to any of the audio coils. It picked off the stereo and the box decoded it and gave line level outputs for a stereo.

It had Dolby NR, synthetic stereo and a few other features.

It worked great, but I gave up on it when VHS' got cheap and cable came to my neighborhood. I went to that method. My CTC9 is delivering fine surround sound today.

Here is one on ebay right now.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3078869946&category=14978

Speaking of stereo, none of the major TV stations (ABC, CBS, NBC) have stereo here! (Odessa/Midland TX.) They are all mono. Only stations that have stereo are the Fox and Univision affiliates.

I used an AM/FM board from a junked gettho blaster and modified the stereo decoder (a chip) to detect TV sound stereo. Easy mod: add a cap to the RC circuit that has the trim pot to tune it to the 15.7KHz pilot. The detected sound has excessive high audio frequencies, which is likely due to differing preemphasis with TV sound vs FM radio. Also, if the bandwidth of the TV IF circuits is too narrow, there will be some "scratchy" distortion products in the L-R signal. Also the signal will need to be stronger.

Originally posted by heathkit tv
Shove come to push you could always run a VCR as the stereo source. This would also give you remote channel selection, just leave the set on ch. 3 of course. Seems to me that this will be the solution to when broadcasters switch to digital.

Anthony

That is exactly how I plan to handle the changeover from analog to high-definition digital, if I still have my two 19" color sets then. I have Comcast digital cable, which uses Dolby digital cable boxes for analog sets (I have one on my RCA XL-100 in my living room). These are likely digital-to-analog converters, so the user's analog TV and VCR remain on channel 3 or 4 to receive the converter's output. The boxes all have remote control, so even if it's connected to a TV with a detented VHF selector, it will convert the set to remote and silent digital tuning/volume/on-off control just like that. Just put the old set's selector on channel 3 or 4 (as we did years ago with UHF converters on older VHF-only sets, only their output was on channel 5 or 6), and there you are. (Saves wear and tear on the old tuner as well.) Just like downtown, even with a 50-year-old set or even a small b&w portable.

The only thing I don't really like about the newest cable boxes, at least Motorola's latest ones (I just had mine replaced by a new model) is that the only way to control them is with the remote; there are no buttons, switches, etc. whatsoever on the box itself. This could put a set owner in a bad situation (no way to operate the cable box, leading to no reception) should the remote cease to function for any reason, including dead batteries. Why didn't Motorola think of that before putting this type of converter on the market? I can only wonder how many cable subscribers have complained to Comcast (and other cable companies using Motorola digital cable boxes) about this. :dunno:

One way around the problem, however, would be to have a universal remote programmed to operate your brand of cable box, so if anything happens to the original remote the user would still have a method of operating the box. Comcast (and probably other cable companies as well) will allow its customers to use their own aftermarket remotes (or the one which came with their TV or VCR) to operate the cable box if the customer so desires, and if the remote is capable of being programmed to operate the box. I have several universal RCA remotes which will operate the cable box on my living-room TV just fine, though I prefer the original remote since it provides for master power control of a TV, VCR and the cable converter itself; one button turns on and off all three units at the same time.

I wrote a research paper on the then-new MTS system in college (circa 1983-84). The main component of the dbx NR (the one most noticeable on undecoded dbx) is 50% dynamic range compression.

Re-tuning, adding a 4.5 MHz SIF Amp (6AU6 or equiv.) and Ratio Detector (6DT6 or equiv.) ahead of the MPX input, and adding an expansion stage (6AT6, etc.) after the L-R Det to the FM-MPX circuit in the RCA RC23 and/or RC30 tube manuals plus building a +180V power supply (built around AES #P-T269EX and 6X4 or equiv. tube) to power it seems quite feasible. The FM-MPX circuit calls for +180V @ 15mA plus heater power for the 12AX7 and 6CL8. Add to that the B+ current demands and heater supply requirements of the other tubes ... 4.5 MHz Amp & Det, Expander, perhaps a 12AU7 as a stereo output buffer (twin cathode follower stages) if desired, and it's all set. The expander input circuit should be driven by the signal across C5 in Circuit 23-10 of the RC23 manual and the expander's output should drive the phase splitter (pin 7 of 12AX7).

Originally posted by Chad Hauris
Speaking of stereo, none of the major TV stations (ABC, CBS, NBC) have stereo here! (Odessa/Midland TX.) They are all mono. Only stations that have stereo are the Fox and Univision affiliates.

In this day and age, Chad, that's amazing. Isn't there a Federal law which required all TV stations in this country to be broadcasting stereo sound by such-and-such date? (I think it was the late 80s or early 90s, if there is/was such a law--the NBC affiliate in Cleveland started broadcasting in stereo in 1986, followed shortly thereafter by the rest of the stations in the area.)

Most TV stations in major U. S. cities have stereo audio these days, whether or not the FCC requires them to. What on earth is holding back the stations in your area from converting to stereo? :dunno: It seems odd, to me anyhow, that only the Fox and Univision stations in Midland/Odessa have stereo sound.